Two Stroke Motocross
Two Stroke Motocross Forum => Technical => Topic started by: jordan83 on February 26, 2010, 04:38:33 PM
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i have an 03 yz250 and my cylinder needs done. is nikasil or sleeving better?
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Depends,
Sleeves can be rebored if there is an issue with a seizure, but there is more friction between the bore and piston which requires richer jetting than a nikasil bore(and potentially less power)
Nikasil do the opposite to above, but can't be rebored if issues with seizures.
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Plating is vastly superior to a sleeve.
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Depends,
Sleeves can be rebored .
The ability to bore a steel sleeve is irrelevant if there are no over-size pistons available for your engine.
A plated cylinder will dissipate heat better than a steel sleeve, and the plating has better oil retention qualities.
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ive posted only couple questions on this forum and ol chokey helpn me with em all. thanks.
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Plating is vastly superior to a sleeve.
I beg to differ. There is a company in England who have spent a few years developing a range of replacement liners for motocross cylinders which they now offer under their own Mitaka brand name. These can be fitted for a similar price to a re-plate but thereafter you can simply re-bore as they have oversize pistons available up to 2mm.
These have been running in the UK now for over two years in large numbers and there have been none of the drawbacks which the manufacturers told us had to be avoided when they moved away from iron liners all those years ago. There is no distortion due to dis-similar metals heating at different rates, there are no hot spots formed in the cylinders due to poor heat transfer, there are no seizures due to supposed poorer lubrication qualities, the longer these things run with no problems the more it looks like the whole plated cylinder thing was just another big mass production con.
The other thing that always confused me about plated cylinders was why they always run them with chrome rings. To conform to engineering principles, if you are running two metal surfaces against each other there should always be one of them softer than the other as this concentrates all the wear on one of them which you then make easily replaceable, it also reduces friction. This would necessitate running cast rings in plated cylinders (which we do with the minibike engines) as the rings then take all the wear (easily replaced), and also has the added benefit that you can have a sezure and frequently get away with a hone as the ring is too "soft" relatively speaking to damage the cylinder. Running chrome rings in plated cylinders is a total contradiction to this and not surprising therefore that it frequently results in destroyed barrels.
Oh, and in case anyone is worried about high revs with an iron liner, we run an 100cc kart with an Iame Sirio engine which revs in excess of 19k, it has an iron liner!
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Depends,
Sleeves can be rebored .
The ability to bore a steel sleeve is irrelevant if there are no over-size pistons available for your engine.
Most sleeve manufacturers (the good ones anyway) will also offer a range of piston sizes to suit their reborable sleeves.
I recently resleeved my sons ktm 65 as the plating failed after just over 65 hrs, I now have a range of pistons sizes up to about 2mm oversize.
All for less than the cost of replating.
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wheres the best pricing for nikasil?
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as far as i'm concerned plating is the only way to go. i'm kinda surprised that some think a sleeve is better. i guess on real small displacement stuff that goes through rings and pistons often a sleeve MAY be better. i say 'may' because unless you get boring and honing done for free sleeved engines cost more at every rebuild. most shops charge around $75 for the first hole. plated bores can have the glaze broken with a scotch brite pad and go back together. there is no down time. as someone who has measured and bored hundreds if not thousands of cylinders over the years i am amazed how true plated cylinder bores remain. i guess if you blow up alot of motors a sleeve would save you the constant replating cost.
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I am fortunate to have MAX POWER near by and trust them to replate my cylinders.I just brought home a big bore 285cc they did for me and the hole (after measuring) is so perfect it' sick.These guy take so much into consideration like bridge relife to squish clerance that you should go through several pistons before you need to do any type of cylinder refreshing.Its allways dirt or a leaking crank seal that usually brings down a 2 stroke! Mantainece is allways your best bet
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One thing that amazes me that never gets mentioned during this argument is that with a sleeve installed and then going to oversize pistons is that you need to machine the powervalves to suit the next oversize. Then when you have gone through a couple of oversize pistons, you are not just up for a new barrel, but new powervalves as well. This is enough for me, along with all the other downsides to resleeving to not even consider it an option. Replate or replace only.
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One thing that amazes me that never gets mentioned during this argument is that with a sleeve installed and then going to oversize pistons is that you need to machine the powervalves to suit the next oversize. Then when you have gone through a couple of oversize pistons, you are not just up for a new barrel, but new powervalves as well. This is enough for me, along with all the other downsides to resleeving to not even consider it an option. Replate or replace only.
Good point. The power valve issue never even crossed my mind. Def just gona go with replating. Thanks guys.
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I'm not an expert on all the nuances here but I was under the understanding that:
Oil builds up between the silicon carbide surface on a nikasil bore naturally. A sleeved bore must have a rather complex plateau honing process utilized to have similar properties. Benefit nikasil
The piston heat gets drawn through the rings to the bore at the bottom of the stroke and nikasil is better than a sleeved cylinder for this. Benefit nakasil
Modern rings aren't chrome they are some type of nitrided steel. While the nickel surrounding the silicon carbine helps alleviate some of the wear characteristics we're still talking about silicon carbide aka an abrasive. The rings are hardened because they would wear too fast otherwise. I've also read the argument that a 4-stroke has better lubrication on the rings than a 2-stroke. Whatever the cause nakasil allows you to run a very hard ring against a very hard bore.
I've never done any testing to validate any of this, it is just what I've read or heard.
My practical experience has been that you have to ignore a lot of signs and have a very catastrophic failure to destroy a nikasil bore. The benefit of having a top end you can replace with nothing other than some simple tools and a 6 pack of beer far outweigh the very infrequent need to send you cylinder in for repairs.
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We've all heard all the reasons for years about how plating was so much better but the fact remains that this company have fitted a helluva lot of liners to modern bikes and there's been no problems and that's difficult to dispute. Theory is fine but I'll go on practical experience (if available) every time.
Another thing which maybe some won't see is that once a crosser becomes a year or two older and drops off the competitive scene, it's owner is more likely to just ride it till it stops. That in most cases will be big-end failure and again, in most cases, the barrel will be totalled by debris from the big end. Then, in UK prices, you're looking at £30 for a re-bore versus £170-180 for a repair and re-plate.
Again, hard to argue with!
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I like sleeves because it's a DIY, if you know what your doing. On the other hand nikasil, you have to send out because it's a custom job. I don't recommend sleeves if you don't have the correct tools, milling machine or if you don't know what your doing. Just my 2 cents. ;D
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We've all heard all the reasons for years about how plating was so much better but the fact remains that this company have fitted a helluva lot of liners to modern bikes and there's been no problems and that's difficult to dispute. Theory is fine but I'll go on practical experience (if available) every time.
Again, hard to argue with!
I'll give you practical experience EVERY time someone uses an iron liner in a cylinder designed for Nikasil they ping their heads off when they get hot. The last poor sod that told me about his WR 250 that had been abused is such a fashion, he was shattered to find out that his cylinder could be welded machined and replated for 2/3rds the cost of a resleeve.
You can also Nikasil over cast iron liner when you are on max piston size.
Show me the 50 odd HP 125 GP or 110HP 250 GP engine that uses cast iron liners ::)
Fixed gear 100cc kart engines are not anything special, an old KT100s engine will go near that, step up to Rotax Max,ICC or Superkarts and you will see the difference between cast and nikasil.
I take old iron liners out and replace them with plated aluminium liners, they handle higher compression ratio's and a cylinder head temp gauge proves they handle heat for longer. Practical enough for you?
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Well if I ever experience any of the difficulties with iron liners that seem to have beset your endeavours then obviously I would be silly not to have a re-think.
But until then, as I have had no difficulties with them, and especially given the cost issue which definately lies in the favour of the liner at UK prices, I'll continue as before.
But thanks for relating your own personal experiences.